Stockholders' Equity (Schedule of tax benefit (expense) on net activity) (Details) (Details) - USD ($) $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended	8 Months Ended	9 Months Ended
	Sep. 30, 2017	Aug. 31, 2017	Sep. 30, 2016	Aug. 31, 2017	Sep. 30, 2016
Successor
Other Comprehensive Income (Loss), Tax	$ 0
Successor | Pension Plan
Other Comprehensive Income (Loss), Tax	0
Successor | Other Post Employment Benefit Plans
Other Comprehensive Income (Loss), Tax	0
Successor | Derivative Instruments
Other Comprehensive Income (Loss), Tax	$ 0
Predecessor
Other Comprehensive Income (Loss), Tax		$ (32)	$ (33)	$ (144)	$ 773
Predecessor | Pension Plan
Other Comprehensive Income (Loss), Tax		(31)	(40)	(145)	668
Predecessor | Other Post Employment Benefit Plans
Other Comprehensive Income (Loss), Tax		(1)	6	(5)	125
Predecessor | Derivative Instruments
Other Comprehensive Income (Loss), Tax		$ 0	$ 1	$ 6	$ (20)